Presently known arrangements providing for intermittent advance of motion picture film for projection of film frames are of mechanical variety on the one hand involving claw-type feeding mechanisms, so-called maltese cross feeding mechanisms, or mechanisms of type illustrated in commonly-assigned U.S. Pat. No. 3,806,246. Such known arrangements are of electro-mechanical variety, on the other hand, such as shown in U.S. Pat. No. 2,994,247, involving electromagnetically operated ratchet mechanisms, or in U.S. Pat. No. 1,888,094, wherein a sprocket assembly is rotated by magnetic coupling thereof to a rotatively driven selectively energized solenoid. Of such known arrangements, the structurally least complex is considered to be that of the referenced commonly-assigned patent, involving axially spaced driven members continuously biased into engagement with a sprocket assembly disposed therebetween with a stop member selectively engaging the sprocket assembly to arrest its rotation.
Apparatus disclosed in a further commonly-assigned patent, U.S. Pat. No. 3,954,214, simplifies the above-discussed arrangements in disposing the film-advancing sprocket between axially-spaced driven members selectively biased into engagement with the sprocket. In its preferred form, such '214 patent includes an electromagnet providing such selective bias condition when energized, the electromagnet being deenergized for film stoppage upon engagement of electrically-conductive sprocket teeth with a cyclically-moved electrically conductive follower element.